This invention relates to a process for preparing 1-amino anthraquinone from the reaction of 1-nitro-anthraquinone with ammonia in water and/or an organic solvent followed by treatment of the 1-amino anthraquinone imine formed with water to convert same into 1-amino anthraquinone.
Processes for the preparation of 1-amino-anthraquinone by reacting 1-nitro-anthraquinone with ammonia in water (R. Oda, J. Soc. Chem. Ind., Japan, 43. Suppl,binding 386 (1940)) and acid amides (German Offenlegungsschrift No. 2,211,411) are known.
The yields of 1-amino-anthraquinone obtained by these processes, however, are not substantially higher than 94 % and 80 % respectively. It is found that when the reaction is carried out in these, as well as in other, organic solvents, e.g. in substituted or unsubstituted aromatic or aliphatic solvents, nitriles, esters, sulphones, ethers and alcohols, the 1-amino-anthraquinone undergoes a secondary reaction to form substantial quantities of 1-amino-anthraquinone monoimine, depending on the reaction conditions.
The formation of 1-amino-anthraquinone imine is particularly pronounced if an excess of ammonia is used for the amination reaction. Such ammonia excess is, however, necessary in order to obtain complete conversion within economical reaction times. The 1-amino-anthraquinone imine formed in this reaction (in the most favourable case 1 to 10 %, based on the quantity of nitro-anthraquinone introduced) reduces the yield of 1-amino-anthraquinone.